Monday, April 9, 2007

Invasive Arthropods

We met the arthropods today and my goodness they are neat! Sally gave us the lightning run down of the whole phylum and two guest lecturers introduced us to the arthropods they are studying. Sylvia Yamada told us about the European green crab, an introduced and potentially ruinous arthropod. She set traps for us and we got to check out a couple different species and even caught two green crabs! They're chilling in the lab, little do they know they will never see the light of day again... hahaha

After lunch, John Chapman (of HMSC) told us all about his pursuit of Orthione griffenis, another introduced arthropod. Orthione griffenis is an isopod parasite of Upogebia pugetensis (those charming blue bay shrimp from the mudflats) that according to John, may have been introduced as early as 1983 in ballast water. These little guys are pretty nasty: what they do is crawl inside the gill cavity of the shrimp and attach themselves there to suck blood right out of the shrimp's carapace. The female isopod can get pretty big, about 24mm. If 24mm doesn't scare you, imagine you are a shrimp, total length about 80mm. That little parasite is bigger than your head! What's worse, the isopods always come in pairs. The male, much smaller, actually lives off the female, latching onto her hips! (more or less)

So what are the implications of this introduced species? Potentially quite great. By removing nutrients from the shrimp, the parasite prevents it from reproducing (hey, if you had a parasite bigger than your head sucking your blood, you wouldn't be in the mood, either). Although some clam diggers might see Upogebia as a pest (their burrowing activities can burry clam recruits), they are extremely important habitat engineers. In an estuary like Yaquina Bay, they can filter up to 80% of the water and their burrows are used by lots of other invertebrates. John's surveys have revealed that 45% of Upogebia in Yaquina Bay (and maybe 80% of the sexually mature adults) are already parasitized by Orthione. So what's next? John is now studying why the parasite causes the shrimp to stop reproducing and how that is going to affect the population of Upogebia and the entire estuarine ecosystem.

You can probably see the male isopod (he's the little white guy). The female pretty much fills the shrimp's gill cavity and she's got a fat pile of eggs. We were able to pull them out with tweasers to get a closer look. Yep, they're pretty nasty. ~Lou

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